As market forces continue to push the limits of efficiency, capacity, and usability of electronic devices, nanoelectronics emerge as a possible response. In particular, nanoscopic devices have been designed and proposed as new paradigms of computer building blocks, optoelectronic switches, optical detectors, biological labeling, energy conversion, storage media, smart coatings, sensors, etc. Common to these proposals is the fact that excess carriers (e.g., electrons, or holes) are typically responsible for much of the devices' functionality. In addition, in many proposed applications, the devices are probed and manipulated with light, as such a probe is contactless and tends to preserve device integrity, and is faster than conventional electronics.
Light interacting with nanostructured metals and (electron- or hole-doped) semiconductors and semimetals can interact with excess electrons present in the material to excite collective electronic charge-density excitations (e.g., surface and bulk plasmons, magnons in magnetic metals and magnetic doped semiconductors, electromagnetic field induced charge redistribution in quantum dots . . . ). Such excitations are non-trivial since they can be affected by quantum confinement effects and surface effects, in addition to many-body effects which tend to be enhanced upon confinement. Moreover, it should be noted that the excitations are quantum mechanical entities, and as such can exhibit both particle and wave nature. Probing and monitoring these electronic excitations, both in real-space and time-domain, poses a challenge to commonplace techniques such as (i) far-field optical microscopy, which is limited by diffraction to resolution of one-half of the optical wavelength (e.g., above 100 nm), (ii) near-field optical microscopy, which has a very low data acquisition rate, and (iii) electron microscopy, which is typically limited by low-intensity incoherent electron sources to video update rates (e.g. nearly 60 Hz).